#include <iostream>
#include <fstream>

using namespace std;

const int NMAX=2000000;
bool c[NMAX+1];

int main() {
    c[1]=1; int n;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin >> n;
    int d, m, i, cnt=0;
    for (d=2; d*d<=n; d++) {
        if (!c[d]) {
            for (m=d*d; m<=n; m+=d)
                c[m]=true;
        }
    }
    for (i=1; i<=n; i++)
        if (!c[i])
            cnt++;
    fout << cnt;
}